True UMS devices support access to the device/player as an external disk drive (universal mass storage). These devices will work with Windows XP, 2000, 98 with driver, Macs, and Linux PCs.

A pure UMS player will support audio file transfer via the disk drive and either provide a self-databasing feature or navigation by folder. The Rio Carbon with recent firmware provides both tag and folder navigation. The Ipods provide UMS support but not for music transfers. The Sansa E2xx players support both MTP (MS's protocol) and UMS music transfers (self-databasing). The Sansa E130 supports self-databasing. Iaudios support UMS music transfers and folder navigation.

Some new players like the CLIX only support MTP (Windows XP) music transfers.

Okay, so it's not true UMS, but it does support some sort of drop and drag feature for transferring music files, right? How does this work?

The reason I'm interested is I currently have a Sansa e260 that I'm considering getting rid of (can't tolerate the poor audio quality using IEM). The thing I like most about the Sansa is that I can drag and drop my folders in UMS mode. Never have to mess with WMP. If I ditch the Sansa, the Zen V Plus looks like an attractive alternative. But I'd still prefer the no fuss, no muss approach to uploading content.